Auto merge of #45198 - oli-obk:fmt_args, r=sfackler

Prevent fmt::Arguments from being shared across threads

Fixes #45197

This is a **breaking change**! Without doing this it's very easy to create race conditions.

There's probably a way to do this without breaking valid use cases, but it would require quite an overhaul of the formatting machinery.

diff --cc src/libcore/fmt/mod.rs
Simple merge